1. Field of the Invention
The present invention relates to a semiconductor laser apparatus with semiconductor laser devices of different wavelengths, and an optical apparatus therefor.
2. Description of the Background Art
With recent enhancements of the performance of personal computers and multimedia equipment, the amount of information to be processed has markedly increased. The increased amount of information has led to the development of optical recording mediums and their drives which can handle increased capacity and high frequency of information processing.
Specific examples of such optical recording mediums include compact disks (which will hereinafter be referred to as CDs) and digital versatile disks (which will hereinafter be referred to as DVDs). Specific examples of the drives that play back and record such optical recording mediums include semiconductor laser apparatuses for CDs and semiconductor laser apparatuses for DVDs. A semiconductor laser apparatus for a CD is capable of emission of an infrared laser beam (wavelength around 790 nm) used in playing back or recording the CD, while a semiconductor laser apparatus for a DVD is capable of emission of a red laser beam (wavelength around 658 nm) used in playing back or recording the DVD.
Among optical recording medium drives is also a semiconductor laser apparatus that can play back or record a CD and DVD. This semiconductor laser apparatus is capable of emission of an infrared laser beam for the CD and a red laser beam for the DVD.
The use of such a semiconductor laser apparatus enables a smaller parts count than the combined use of a semiconductor laser apparatus for a CD and a semiconductor laser apparatus for a DVD, resulting in a simpler optical recording medium drive.
Meanwhile, in order to enhance the recording density in optical disk systems, the development of semiconductor laser devices for next-generation DVDs which emit blue-violet laser beams with short wavelength (a lasing wavelength of around 400 nm) is progressing. A semiconductor laser apparatus has also been developed which incorporates such a semiconductor laser device that emits a blue-violet laser beam (refer to JP 2001-230502 A).
In the specification, a semiconductor laser device that emits a blue-violet laser beam will be referred to as a blue-violet semiconductor laser device, a semiconductor laser device that emits an infrared laser beam will be referred to as an infrared semiconductor laser device, and a semiconductor laser device that emits a red laser beam will be referred to as a red semiconductor laser device.
Now, the semiconductor laser apparatus as described in JP 2001-230502 A will be illustrated. FIG. 29 is a schematic diagram showing the semiconductor laser apparatus described in JP 2001-230502 A.
As shown in FIG. 29, a blue-violet semiconductor laser device 901 is bonded onto a support base 903a integral with a package body 903 with a fusion layer 905 interposed therebetween. The blue-violet semiconductor laser device 901 is mechanically, electronically connected with the support base 903a. 
An infrared semiconductor laser device 902a and a red semiconductor laser device 902b are bonded onto electrodes 901a, 901b, respectively, of the blue-violet semiconductor laser device 901 via fusion layers 906, 907.
The infrared semiconductor laser device 902a and red semiconductor laser device 902b form an integrated semiconductor laser device 902 that is monolithically integrated on the same substrate. In this case, in order for either of the infrared semiconductor laser device 902a or red semiconductor laser device 902b to operate independently, the electrode 901a connected with the infrared semiconductor laser device 902a is formed on the blue-violet semiconductor laser device 901 with an insulating layer 904 therebetween. Power supply pins 909a, 909b, 909c are formed so that they are electrically isolated from the package body 903 through insulating rings 908a, 908b, 908c. An electrode 902c is formed on the upper surface of the integrated semiconductor laser device 902.
The electrodes 901a, 901b, 901c, respectively, are connected to the power supply pins 909a, 909c, 909c through wires 910a, 910b, 910c. The support base 903a receives power from the power supply pin 903b which is connected to the package body 903.
With this structure, the semiconductor laser apparatus can emit any one of an infrared laser beam, a red laser beam, or a blue-violet laser beam selected.
However, for the blue-violet semiconductor laser device 901 that emits a blue-violet laser beam having short wavelength, the lasing threshold voltage is higher than that of the infrared semiconductor laser device 902a that emits an infrared laser beam having long wavelength or the red semiconductor laser device 902b that emits a red laser beam. Such high lasing threshold voltage is attributed to the materials forming the blue-violet semiconductor laser device 901.
FIG. 30 is a circuit diagram of the semiconductor laser apparatus of FIG. 29.
As shown in FIG. 30, in order to drive the blue-violet semiconductor laser device 901 with a high lasing threshold voltage, it is necessary to apply a high voltage to the other power supply pin 909b with respect to the package body 903 which is commonly grounded when used. This precludes the use of a drive circuit available at relatively low cost, which has been conventionally employed to drive the infrared semiconductor laser device 902a and red semiconductor laser device 902b in the semiconductor laser apparatus of JP 2001-230502 A, resulting in a necessity of employing a new drive circuit that can handle high voltage.